Galvanomagnetic, Optical Properties and Ultraviolet Photoelectron Spectra of Potassium-Oxygen-Graphite Intercalation Compounds

We investigated the Hall effect, the transverse magnetoresistance, the optical reflectivity and the ultraviolet photoelectron spectra for 1st and 2nd stage KO_x-GICs (C_4nKO_x, stage number n = 1,2; x∼2) in order to clarify the transport properties and the electronic structures. The Hall effect and the magnetoresistance indicate that the electrical conduction in KO_x-GICs is governed by the majority electron carriers with low mobility in graphitic π bands and the minority hole carriers with high mobility in the intercalate bands, the latter of which originates mainly from the oxygen bands as suggested by the incident photon energy dependence of the ultraviolet photoelectron spectra. The optical reflectance spectra give the estimates of the Fermi energies, 1.9 eV and 1.35 eV for 1st and 2nd stage compounds, respectively, on the basis of the Drude-Lorentz model. The contribution of the intercalate hole carriers to the plasma frequency is small in good agreement with the Hall effect indicating the presence of minority hole carriers. These experimental findings suggest the contribution of the intercalate layer to the transport properties and the electronic structure around the Fermi level.